Abstract:
The need for sensitive, affordable, and user-friendly sensing technologies for disease diagnosis and drug discovery is always in high demand. Especially, diagnosis of infectious disease at its early stage is important for timely anti-infectious treatment and prevention of the further spread of infection. In most cases, the early diagnosis is achieved by detecting the molecular biomarkers specific to the infection (host derived or pathogen derived) in bodily fluids of the infected subjects. The conventional chemiluminescent immunoassay (CLIA) technique is limited by turn-around time and requirement of sophisticated infrastructure and skilled personnel. The state-of the art lateral flow assay (LFA) technology based point-of-care (PoC) diagnostics lacks sensitivity for a reliable diagnosis. Over the past decades, several optical sensing strategies (e.g. plasmonic and gratings based resonance, and interferometry) have been explored to realise sensitive point-of-care tests (PoCT). Fiberoptic sensors (FOS), especially U-bent fiber sensor platform, offer several advantages including high evanescent wave absorbance (EWA) sensitivity, ergonomic design and a simpler instrumentation for affordable PoCT. This thesis utilizes the U-bent sensor probes to develop a plasmonic fiberoptic absorbance biosensor (P-FAB) for the highly sensitive detection of molecular biomarkers.
P-FAB exploits the high evanescent wave absorbance (EWA) sensitivity of U-bent fiberoptic probes and extinction of gold nanoparticles to realize plasmonic sandwich immunoassay schemes with a pair of LED-Photodetector based optical instrumentation. In the process of realizing a sensitive P-FAB, optimum conditions such as fiber probe geometry (core and bend diameter), surface functionalization, fiber probe material, AuNP size, and their bioconjugation, and AuNP label concentration were investigated in detail. The U-bent sensor probes with a bend ratio of 3 (ratio of bend diameter to core diameter) were found to have high EWA sensitivity compared to larger ratios such as 5, 7, and 15. It was also found that EWA response improves with a reduction in the core diameter, which could be attributed to the improved depth of penetration and decreased width of propagation. Besides optimizing the probe geometry, novel surface modification strategies for functionalizing inert PMMA core of the plastic optical fiber (POF) were investigated. The results showed that the HMDA-based POF surface functionalization remains superior to globular poly(amidoamine) dendrimer molecules and two-dimensional graphene oxide (GO) nanostructures.
To achieve a highly sensitive P-FAB, influence of fiber probe material (POF and fused silica optical fiber probe, GOF), AuNP label size (20, 40, 60, and 80 nm), and concentration (2×, 10×, and 20×) were investigated. The GOF sensor probe combined with 60 nm AuNP label at 20× concentration gave rise to relatively higher sensitivity for P-FAB compared to other combinations. The optimized P-FAB strategy was utilized to realize a P-FAB for TB as well COVID-19 disease biomarkers, including mannosylated lipoarabinomannan (ManLAM or Mtb-LAM) down to 1 fg/mL (59 aM) and 10 fg/mL (590 aM) in the buffer and synthetic urine, and 2.5 ng/mL (~55 pM) of SARS-CoV-2 N-protein, respectively. The results obtained were utilized to translate the laboratory set-up to a hand-held PoC P-FAB device, which was validated and demonstrated to detect of varying concentrations of Mtb-LAM and SARS-CoV-2 N-protein. In summary, the successful demonstration of P-FAB technology shows that this can be a universal platform for the development of PoC diagnostics for many other diseases.
Publications:
1. Divagar, M., Gayathri, R., Rasool, R., Shamlee, J.K., Bhatia, H., Satija, J. and Sai, V.V.R., 2021. Plasmonic Fiberoptic Absorbance Biosensor (P-FAB) for Rapid Detection of SARS-CoV-2 Nucleocapsid Protein. IEEE Sensors Journal.
2. Divagar, M, Bandaru, R., Vani, J. and Sai, V V R, 2020. A Plasmonic Fiberoptic Absorbance Biosensor for Mannose-capped Lipoarabinomannan based Tuberculosis detection, Biosensors and Bioelectronics, 167, pp. 112488.
3. Divagar, M., Himanshu, B., Satija, J. and Sai, V.V.R., 2020. P-FAB: A fiber optic biosensor for rapid detection of COVID-19, Transactions of INAE, 10.1007/s41403-020-00122-w
4. Bandaru, R., Divagar, M., Shruti, K., Shalini G., Vani, J. and Sai, V.V.R., 2020. U-bent fiber optic plasmonic biosensor platform for ultrasensitive analyte detection, Sensors and Actuators B: Chemical.
5. Klages, C.P., Raev, V., Murugan, D. and Sai, V.V.R., 2020. Argon–water DBD pretreatment and vapor‐phase silanization of silica: Comparison with wet‐chemical processes. Plasma Processes and Polymers, p.e1900265.
6. Divagar, M., Saumey, J., Satija, J. and Sai, V.V.R., 2019. Self‐Assembled Polyamidoamine Dendrimer on Poly (methyl meth‐acrylate) for Plasmonic Fiber Optic Sensors. ChemNanoMat, 5(11), pp.1428-1436.
7. Rajamani, A.S., Divagar, M. and Sai, V.V.R., 2019. Plastic fiber optic sensor for continuous liquid level monitoring. Sensors and Actuators A: Physical, 296, pp.192-199.
8. Divagar, M., Gowri, A., John, S. and Sai, V.V.R., 2018. Graphene oxide coated U-bent plastic optical fiber based chemical sensor for organic solvents. Sensors and Actuators B: Chemical, 262, pp.1006-1012.